The present disclosure belongs to the area of protecting an airborne platform against collision.
The disclosure is more particularly aiming at detecting short range obstacles over a wide field of view. This field of view may cover at least 180° horizontally in order to survey the rear part of the platform which is not observable by the pilot, if the airborne platform is piloted. This field of view will encompass parts of the fuselage of the airborne platform.
The whole field of view has to be surveyed continuously, and not sequentially, in order to minimize the warning time and hence allow sufficient reaction time for the pilot.
In operational scenarios of the disclosure, the airborne platform is stationary or moving at very low speed. Consequently, the obstacles to be detected are located at close range, at the order of magnitude of the airborne platform dimension.
In order to avoid a high false alarm rate which would consequently have the system rejected by the pilot community, the detected obstacles have to be localized with high accuracy.
State of the art radars for obstacle detection have been developed in the automotive domain.
The wide field of view requirement is fulfilled by using several sensors, covering segments of the whole field of view. The sensors are arranged so that a given sensor never receives echoes of signals emitted by another sensor which are reflected by the automotive platform itself.
This is no longer the case for an airborne platform where moving parts of the fuselage, such as rotor blades of a helicopter platform, will be permanently in view of sensors, creating spurious signals generated by one sensor transmitter and reflected into the other sensor receiver.
The range accuracy requirement is fulfilled by the use of Ultra Wide Band frequency of operation. Moreover, Ultra Wide Band frequency allows shifting in frequency automotive sensors, as proposed in document EP 2 180 336 A2, so that two sensors located in close proximity do not interfere with each other, while maintaining sufficient bandwidth for each sensor in order to fulfill the range accuracy requirement.
Shifting sensors in frequency, i.e. operating at different frequency ranges (sub-band) in the same bandwidth, as proposed in document EP 2 180 336 A2 is no longer possible in airborne domain where the use of Ultra Wide Band frequency is strictly prohibited by frequency regulation authorities. Airborne sensors have to conform to ITU regulations where the authorized bandwidth, especially for airborne application, is relatively narrow so that each sensor has to use the whole frequency band in order to provide the accuracy required by the collision avoidance application at low speed.
Having the sensors operating sequentially in time degrades the detection refresh rate over the whole field of view and do not allow sufficient warning time for the pilot to avoid the collision.
The frequency used in automotive sensors is high, so that high directionality is achieved with small sensors. This helps to prevent interference between sensors, and allows easy azimuth direction estimation.
This is no longer the case in airborne sensors as the available frequency band is much lower, so that small sensors will have a wide radiated beam.
One object of the disclosure is to overcome these limitations.